Daylight harvesting is an available lighting strategy designed to reduce excessive internal light levels during peak consumption hours, wherein external light sources such as daylight substitute for interior electrical lighting. For example, in an office setting, each work area must at all times be provided with a minimum level of light which is determined based upon the tasks performed in the area or zone. Lighting, however, is generally installed by size and number sufficient to provide the minimum light level under the assumption that no other light sources are available in the interior space. Yet, during varying times of the day, other light sources may illuminate the interior space such that the resulting level of light present is excessive. Therefore, the use of interior lighting at the same level of intensity without any regard for the additional sources of lighting becomes a waste of energy.
Specifically, during the day, sunlight may enter through windows and other openings such as skylights. When these external light sources are present, the preset brightness of the interior lighting may not be necessary since the external light sources provide some or all of the minimum light level required. Daylight harvesting eliminates the excessive level of intensity of interior lighting, conserving as much as 84% of the energy required to light a facility at the minimum light level. Relatively bright sunlight, however, can provide at times up to 100% of the required illumination—especially during midday, when energy costs are highest.
Daylight harvesting also enables a constant level of light on work surfaces to avoid moments when the additional sources of light i.e., external light sources, provide an excessive amount of light, resulting in periods of glare. In the alternative, when light levels are low (i.e. when clouds roll in or nighttime falls), daylight harvesting maintains this constant level of light by continuously increasing and/or decreasing (i.e., adjusting) the power applied to the internal lighting. This practice enables a worker in the lighted environment to resolve images with ease. As a result, eyestrain is avoided; and health and productivity are promoted.
Conventional technology for implementing daylight harvesting techniques incorporates the use of digital photo-sensors to detect light levels, wherein the digital photo-sensor is connected to a dimmer control circuit to automatically adjust the output level of electric lighting for promotion of a lighting balance. Dimmer control circuits, as implemented with respect to daylight harvesting, gradually adjust (i.e., increase or decrease) interior lighting in response to photocell measurement of ambient light levels.
In general, dimmer control systems are widely used in indoor lighting to provide a softer feel and more controllable illumination experience as compared to on/off lighting. It is desirable to provide dimmer control systems for fluorescent as well as for incandescent lighting. Conventional dimmer control circuits include on/off switching and up/down power controls. Further, a microprocessor may be incorporated within a dimmer control circuit to provide control for various power-up, power-down and fade in/out functions. Rather than use a variable resistor type rheostat which wastes power and generates heat at low illumination levels, modern dimming control circuits employ phase regulation, in which the power circuit is switched on at a time delay following a zero-crossing of the AC sine wave input until the end of each half cycle, in an effort to supply a variable level of power to the lighting load. For dimming control in fluorescent lamps. a ballast with a controlled low voltage (0-10 V) input is desired.
In conventional low voltage switch systems that do not incorporate features, such as dimming and daylight harvesting, two states exist for each input: ground or 0 volt and a non-zero voltage which is typically +24 volts. Two button switches are known in the industry and are standard. They provide ON and OFF inputs. Many light switch manufacturers in the industry develop most of their products to include an ON and OFF input for each switch control input. One approach for increasing the functionality of a low voltage switch uses three states, wherein each input, ON and OFF, are configured to receive 0 volts or a low voltage, a mid-voltage, and a high voltage. Therefore, given a conventional +24 volt system, the voltage states applied to each input include voltage levels of 0 volt, 12 volts and 24 volts.
In accordance with provisions for light control systems having daylight harvesting and dimming features, Leviton Manufacturing Co. manufactures a multi-button switch, product model CN200, having five buttons (ON, MAX, BRIGHT, DIM and OFF) for switching one or more electrical loads. The ON button turns the lights fully on and activates a daylight harvesting scheme. The OFF button turns the lights off. The MAX button turns the lights on at full brightness and disables the daylight harvesting feature. Finally, the BRIGHT and DIM buttons raise and lower the lighting levels while disabling the daylight harvesting feature. Under typical low voltage switch technology, however, separate inputs and circuitry are necessary to implement such features in a light switch control device similar to that described above. Thereby, the associated cost of components and wiring are increased with each feature.
Thus, there exists a need for a simple, yet, effective design of a multi-button low voltage adaptable switch that may be implemented using the two input switch control system having three input states that mimics the functionality of a light control switch system including features such as dimming and daylight harvesting.
The present invention is directed to overcoming, or at least reducing the effects of one or more of the problems set forth above.